THE COMPARISON OF INJURY SEVERITY INSTRUMENT PERFORMANCE USING LIKELIHOOD RATIO AND ROC CURVE ANALYSES

Background: The relative merits of injury severity instruments are oft en difficult to determine because the statistical techniques, study po pulations, and outcomes used in trauma research tend obscure rather th an elucidate differences in performance. Objective: To describe the ad vantages of likelihood ratio and receiver operator characteristic (ROC ) curve analyses and to demonstrate them using study populations and o utcomes that facilitate instrument discrimination. Materials and Metho ds: Previously published data on the performance of the ''Injury Sever ity Score'' and of four triage instruments in the prediction of mortal ity; paired comparison of two instruments in a previously unpublished trauma registry dataset; use of likelihood ratio and ROC analyses. Mea surements and Main Results: In a comparison of triage instruments this study clearly showed that CRAMS, PHI, and RTI, which contain nonphysi ological information, have higher performance levels than the Revised Trauma Score (RTS), which is restricted to physiological information, Absolute performance gains of these instruments over the RTS ranged fr om 5.9% to 43.5%. This study also noted that the ISS performs equally well for blunt and penetrating trauma, and affirms concerns about the adequacy of its performance Conclusions: Likelihood ratio and ROC curv e analyses demonstrate differences in injury severity instrument perfo rmance that were obscured by less rigorous methods of comparison.